The Registry for Research on Hormonal Transplacental Carcinogenesis continues its investigation of the epidemiology, pathogenesis, biologic characteristics, management and prognosis ofhuman genital cancers that develop after intrauterine exposure to exogenous sex hormones. A computerized data bank that contains carefully monitored and doubly checked details for each case forms the basis for this research. Active canvassing of treatment centers and tumor registries will continue in order to obtain all cases of clear cell adenocarcinoma of the genital tract occurring in females born after 1940, with or wothout a history of hormone exposure, as well as all cases of other types of genital cancer that develop in individuals exposed to either diethylstilbestrol (DES) or any other type of sex hormones including those of steroidal nature. Detailed clinicopathologic correlative studies will be directed toward a wide variety of host and cancer characteristics that may be related to the behavior of the tumor (i.e., histology, depth of invasion, mitoses, grade and location). A particular interest exists in squamous cell carcinomas of the vagina and cervix that arise in the exposed. The investigation of lesions that precede clear cell adenocarcinoma will continue. Knowledge of treatment and prognosis of these lesions will be expanded. We shall remain a source of scientific information and consultation for this problem.